1. Field of the Invention
The present invention relates to a composite carbonate useful as a raw material for producing a lithium nickel manganese cobalt composite oxide to be used in a positive electrode active material for use in a lithium secondary battery and a method for producing the composite carbonate.
2. Description of the Related Art
Lithium cobaltate has hitherto been used as a positive electrode active material for a lithium secondary battery. However, lithium nickel manganese cobalt composite oxides low in cobalt content have been developed because cobalt is a rare metal.
In these years, there have been demanded batteries excellent in rapid charge properties to be used in electric automobiles and power tools such as electric tools. Although increase of the specific surface area of the positive electrode material is a technique to cope with rapid charge, lithium nickel manganese cobalt composite oxides having hitherto been developed are all small in specific surface area.
Most of conventional methods for synthesizing lithium nickel manganese cobalt composite oxides use as starting raw materials nickel manganese cobalt composite hydroxides; the raw materials are small in specific surface area, and consequently, lithium nickel manganese cobalt composite oxides obtained therefrom are also small in specific surface area.
On the other hand, methods using as starting raw materials nickel manganese cobalt composite carbonates have also been proposed. Proposed examples of the method for producing a nickel manganese cobalt composite carbonate include the following two methods: the method of Japanese Patent Laid-Open No. 2001-148249 (p. 7, p. 9) (Patent Document 1) in which a solution that contains sulfates of nickel, manganese and cobalt and an aqueous solution that contains ammonium bicarbonate are simultaneously or alternately added dropwise to a water-containing solution to conduct the reaction while the pH of the solution is being controlled to fall within a range from 6.5 to 8.5; and the method of Japanese Patent Laid-Open No. 2006-117517 (p. 7) (Patent Document 2) in which a solution that contains sulfates of nickel, manganese and cobalt and an aqueous solution that contains sodium carbonate are simultaneously added to a water-containing solution to conduct the reaction.
However, the composite carbonates obtained by the production methods disclosed in above-described Patent Documents 1 and 2 are 40 m2/g or more in the BET specific surface area as the case may be but are as small as less than 1.7 g/ml in tap density, and accordingly suffers from a problem that the lithium composite oxide produced by using the composite carbonate gives a low filling density of the positive electrode active material in an electrode fabricated with the composite carbonate. Thus, there has been demanded development of a nickel atom-, manganese atom- and cobalt atom-containing composite carbonate that is high in specific surface area and large in tap density, and useful as a raw material for producing a lithium nickel manganese cobalt composite oxide to be used in a positive electrode active material for use in a lithium secondary battery.
Accordingly, an object of the present invention is to provide a nickel atom-, manganese atom- and cobalt atom-containing composite carbonate that is high in specific surface area and large in tap density, and useful as a raw material for producing a lithium nickel manganese cobalt composite oxide to be used in a positive electrode active material for use in a lithium secondary battery, and to provide a method for industrially advantageously producing the composite carbonate.